Renal tubular acidosis is highly prevalent in critically ill patients

Abstract

Introduction: Hyperchloremic acidosis is frequent in critically ill patients. Renal tubular acidosis (RTA) may contribute to acidemia in the state of hyperchloremic acidosis, but the prevalence of RTA has never been studied in critically ill patients. Therefore, we aimed to investigate the prevalence, type, and possible risk factors of RTA in critically ill patients using a physical-chemical approach.

Methods: This prospective, observational trial was conducted in a medical ICU of a university hospital. One hundred consecutive critically ill patients at the age ≥18, expected to stay in the ICU for ≥24 h, with the clinical necessity for a urinary catheter and the absence of anuria were included. Base excess (BE) subset calculation based on a physical-chemical approach on the first 7 days after ICU admission was used to compare the effects of free water, chloride, albumin, and unmeasured anions on the standard base excess. Calculation of the urine osmolal gap (UOG)--as an approximate measure of the unmeasured urine cation NH4(+)--served as determinate between renal and extrarenal bicarbonate loss in the state of hyperchloremic acidosis.

Results: During the first week of ICU stay 43 of the patients presented with hyperchloremic acidosis on one or more days represented as pronounced negative BEChloride. In 31 patients hyperchloremic acidosis was associated with RTA characterized by a UOG ≤150 mosmol/kg in combination with preserved renal function. However, in 26 of the 31 patients with RTA metabolic acidosis was neutralized by other acid-base disturbances leading to a normal arterial pH.

Conclusions: RTA is highly prevalent in critically ill patients with hyperchloremic acidosis, whereas it is often neutralized by the simultaneous occurrence of other acid-base disturbances.

Trial registration: Clinicaltrials.gov NCT02392091. Registered 17 March 2015.

Figures

Figure 1

Daily assessment of the acid-base state during the first 7 days after ICU admission. Forty-three of the patients presented with hyperchloremic acidosis on one or more days. In 31 patients hyperchloremic acidosis (HCA) was associated with renal-tubular acidosis (RTA) characterized by a urine osmolal gap (UOG) ≤150 mosmol/kg and a preserved renal function. The majority (23 of 31) of patients with RTA presented with RTA type II, while 8 of 31 patients showed characteristics of RTA type I. In 26 of the 31 patients with RTA, metabolic acidosis was neutralized mainly by simultaneously decreased plasma albumin leading to a neutral arterial pH. *On one or more days during the first week after admission; #glomerular filtration rate (GFR) ≥25 ml/min.

Figure 2

Standard base excess (SBE) and base excess subsets on days with and without renal tubular acidosis. Forty-three percent of the patients (86 of 373 patient days) presented with hyperchloremic acidosis on one or more days represented as pronounced negative BEChloride. However, this was frequently neutralized mainly by simultaneously decreased plasma albumin levels resulting in positive BEAlbumin and partly by positive BEUMA leading to a neutral arterial pH. In 26 of these 43 patients (55 of 373 patient days) hyperchloremic acidosis was associated with RTA characterized by a UOG of less than 150 mosmol/kg in combination with a preserved renal function. BEAlbumin, base excess attributable to changes of plasma albumin; BEChloride, base excess attributable to changes of plasma chloride; BESodium, base excess attributable to changes of free water; BEUMA, base excess attributable to unmeasured anions; RTA, renal tubular acidosis; UOG, urine osmolal gap.